1. Field of the Invention
This invention relates to detecting information and more particularly relates to detecting a periodic sequence.
2. Description of the Related Art
In magnetic tape drives, periodic sequences are used to track spatial coordinates such as the lateral and longitudinal position on tape. These spatial coordinates are used to adjust the tape servo head to nominal positions on tape or to adjust the tape velocity to a specified target value. In a similar manner, the physical location on tape can be encoded into the periodic sequence allowing the tape system to precisely position the tape to a target location. A tape drive servo system may track the position of the head and tape by decoding the periodic sequence for one or more instances of the periodic sequence as is well known to those skilled in the art.
The periodic sequence may comprise a plurality of values. The values may be configured as groups of binary data values. The values may repeat every specified number of values. For example, a periodic sequence may include the values ‘1,’ ‘2,’ and ‘3’ and repeat every four values such as ‘1 2 3 3 1 2 3 3.’
The periodic sequence may also be recorded on a storage medium such as magnetic videotape, magnetic hard disk, an optical storage medium, and the like. The periodic sequence may indicate a specified position for encoded information. For example, the periodic sequence may define a position of data encoded on the magnetic data tape. A read channel may employ the position data from the periodic sequence to identify and recover data on the magnetic data tape.
Unfortunately, the periodic sequence may become corrupted. For example, the periodic sequence may be generated with one or more erroneous values. Alternatively, the periodic sequence may be corrupted when stored on the storage medium and/or when read from the storage medium.
In the past periodic sequence values have been correlated with one or more instances of the periodic sequence to determine an observed periodic sequence instance. Unfortunately, correlation may be insufficiently robust to recover the periodic sequence when multiple errors are present and/or when only a small sample of the periodic sequence values is available.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that robustly detects a periodic sequence. Beneficially, such an apparatus, system, and method would improve the recovery of information encoded in the periodic sequence.